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US2828264A - Manufacture process of permanent magnets from sintered mixtures of oxides - Google Patents

Manufacture process of permanent magnets from sintered mixtures of oxides Download PDF

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Publication number
US2828264A
US2828264A US533577A US53357755A US2828264A US 2828264 A US2828264 A US 2828264A US 533577 A US533577 A US 533577A US 53357755 A US53357755 A US 53357755A US 2828264 A US2828264 A US 2828264A
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Prior art keywords
chromium
mixture
oxides
magnetic
permanent magnets
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Expired - Lifetime
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US533577A
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English (en)
Inventor
Medvedieff Serge
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Audax Industries SA
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Audax Industries SA
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C04B35/2683—Other ferrites containing alkaline earth metals or lead

Definitions

  • the invention relates to permanent magnets constituted by sintered mixed oxides of iron and of one or more of the metals barium, strontium, calcium and lead, incorporating oxide of chromium.
  • the ferromagnetism of the ferrites of the alkaline-earth metals and of lead has been known for several decades.
  • the chromium ions form an integral part of the crystalline lattice of the mixed oxides formed at temperatures of between 900 C. and 1400 C. as is confirmed by the displacement of the Curie point.v Oxides of .iron (Fe O and of chromium (Cr O and barium carbonate (BaCO have been mixed in proportions that are suitable for obtaining the molecular ratios Fe/Cr hereinafter indicated, and then finely ground in a ball mill for fourteen hours. The mixture was dried, sifted and compressed into the form of rods, having a diameter of 1 cm. and a length of from 1 to 2 cms., which were baked at 1200 C. for one hour. With the proportion of barium oxide remaining the same, the Curie point was taken for different proportions Fe/Cr:
  • the magnets according to the invention can be prepared by using, as initial material, ferric oxide (Fe O and barium chromate. An intimate mixture of these compounds in the suitable proportions .is made by grinding The powder is dried,
  • the range of molecular proportions Fe/Cr hereinbefore given as between 6 and 12 may be greater, for example between 4 and 20.
  • the crystals of the mixed oxides of iron, of chromium and of an alkalineearth metal are magnetically anisotropic and have (1) A magnetic anisotropy due to the existence of an axis of easy magnetisation which, in the present case, is the senary axis.
  • grains of the compound according to the invention which are placed in an homogeneous magnetic field, become aligned in a direction which is the resultant of the two above anisotropy axes; if the crystallisation of the initial mixture has been suitably regulated, the product obtained is composed of essentially mono-crystalline fine particles for which the axes are coincident.
  • the residual magnetism is three times as great as in the first case.
  • permanent magnets are made with the powders hereinbefore described by aligning the grains of these powders before the sintering treatment.
  • the manufacture of the permanent magnets according to the invention is carried out as follows:
  • Ferric oxide and barium chromate are mixed in one of the foregoing proportions, for example in the proportion Fe O 1BaCrO
  • the mixture is ground in water in .a ball mill for to 14 hours.
  • the ground mixture is drained and dried and then compresed into the form of cakes having, for example, the following dimensions: diameter 8 centimeters, height 2 to 3 centimeters.
  • This coarse powder is ground with water for a time of between 4 and 14 hours, for example, for six hours.
  • the paste or sludge is kept and, after addition of a suitable binder, is used for preparing oriented magnets.
  • the apparatus comprises a coil 1, through which a direct current passes, and a magnetic circuit comprising a central hollow post 2 constituting the core of the coil, a cylindrical part 3 coaxial with the said post, a base 4 connecting the post 2 with the cylinder 3, and a lid 5 having therein a hole in which a ring 6 is fitted.
  • the central post 2 is surmounted by a pole head 7 which, with the ring 6, bounds an air gap in which the lines of force are radial.
  • a plate 8 made of bronze or other non-magnetic metal and having holes 9 therein.
  • a second plate 10 also made of non-magnetic metal and, together with the former plate, defining an exhaust chamber 11.
  • the plate 10 is funnel-shaped and is joined to the central post 2 in a zone in which holes 12 bring the exhaust chamber 11 into communication with the passage 13 provided in the central post.
  • the passage 13 may be put into communication with a vacuum pump.
  • the bottom of the annular space between the members 6 and 7 is covered with a filter cloth and the mould thus formed is filled with paste.
  • the radial magnetic field is applied by passing current through the coil '1 and the water is removed by putting into operation the vacuum pump connected with the passage 13.
  • the field is cut 0E and the assemblage comprising the members 6 and 7 and the paste is removed; After a partial drying of the compressed paste, the latter is subjected, in the mould itself, to a compression of the order of one ton per square centimeter. -After removal from the mould, a piece in the form of a ringis obtained, one of the poles of which is spread over the inner cylindrical surface and the other is spread over the outer cylindrical surface. The particles are therefore oriented radially.
  • the compressed piece is then subjected to baking in an electric furnace for a time varying from half an hour to one hour and to a slow cooling. A sintered ceramic piece is thus obtained which has a density of between 4.5 and 5 gms.
  • a parallel magnetisation that is to say magnets in the form of parallelepipeds or of discs 17 (Fig. 3), the north and south poles of which are situated respectively on two parallel faces 18 and 19, the apparatus represented in Fig. 4 is employed.
  • the apparatus comprises a magnetic circuit 20 which produces a magnetic field of some thousands of oersteds between the plane faces opposite an upper piston 22 and a bottom cylindrical stand 23 made of steel.
  • the piston 22 slides inside a thick tube 24 which is made of nonmagnetic metal and in which the stand 23 is encased.
  • the bottom stand 23 is provided with holes 25 and is connected to a vacuum pump through piping 26.
  • a filter cloth 27 is arranged on the top face of this perforated stand; the fluid paste is poured into the mould constituted by the tube 24; the piston 22 is engaged in the tube, the field is applied and the vacuum pump is set in operation.
  • the forces of magnetic attraction in the ari gap exert a first compression on the paste and accelerate the filtration.
  • the forces, to which the particles are subjected increases with the compression.
  • the force of an hydraulic press giving a pressure of one ton per square centimeter, is applied to the piston.
  • the disc of oriented material although possessing a cohesion which is sufficient for the manipulations (owing to the previously incorporated binder), is still damp. It is dried in order to eliminate first the moisture and then the binder. Finally, it is subjected to baking under the same conditions as in the case of the radial magnetisation. The magnetic characteristics are the same.
  • the temperature and pressure values which have been given depend upon the molecular ratio which, as has been seen, may vary from 4 to 20 and are not critical. A pressure of between 1 and 4 tons per square centimeter and a temperature of between 900 and 1400 C. are allowable.
  • a process for preparing an anisotropic permanently magnetic barium chromium ferrite having a density of at least aboutv 4.45 comprising mixing Fe O with a member of the group consisting of BaCr and a mixture of BaCO and Cr O as will form BaCrO the molecular proportion of iron to chromium being between 4 and 20, pressing said mixture to a temperature of between about 900" C. and about 1400 C. and subjecting said pressed mixture to a steady magnetic field to provide a shaped permanent magnet having a residual induction of at least about 1800 gauss and a coercive force of mag netization of at least about 3200 oersteds.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Hard Magnetic Materials (AREA)
  • Manufacturing Cores, Coils, And Magnets (AREA)
US533577A 1954-11-09 1955-09-12 Manufacture process of permanent magnets from sintered mixtures of oxides Expired - Lifetime US2828264A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR1114010T 1954-11-09

Publications (1)

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US2828264A true US2828264A (en) 1958-03-25

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US (1) US2828264A (fr)
FR (2) FR1114010A (fr)
GB (1) GB781633A (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2946753A (en) * 1955-08-10 1960-07-26 Philips Corp Ferromagnetic material
US2946752A (en) * 1955-08-10 1960-07-26 Philips Corp Ferromagnetic material
US2955085A (en) * 1955-08-10 1960-10-04 Philips Corp Ferrites of decreased initial permeability at high frequencies
US2980617A (en) * 1956-03-13 1961-04-18 Indiana General Corp Ferrite compositions and method of making same
US3023166A (en) * 1956-08-18 1962-02-27 Philips Corp Magnetic record carrier
US5648039A (en) * 1992-04-24 1997-07-15 Tdk Corporation Process for the production of anisotropic ferrite magnets
US5945028A (en) * 1992-04-24 1999-08-31 Tdk Corporation Hexagonal system ferrite particles and their production process

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1283730B (de) * 1963-12-23 1969-02-20 Siemens Ag Vorrichtung zur Herstellung von Formkoerpern, die einer Sinterung unterworfen werden

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1997193A (en) * 1930-12-25 1935-04-09 Mitsubishi Electric Corp Permanent magnet and method of manufacturing same
US2579267A (en) * 1947-12-31 1951-12-18 Rca Corp Material having improved magnetic property
US2762778A (en) * 1951-12-21 1956-09-11 Hartford Nat Bank & Trust Co Method of making magneticallyanisotropic permanent magnets
US2762777A (en) * 1950-09-19 1956-09-11 Hartford Nat Bank & Trust Co Permanent magnet and method of making the same

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1997193A (en) * 1930-12-25 1935-04-09 Mitsubishi Electric Corp Permanent magnet and method of manufacturing same
US2579267A (en) * 1947-12-31 1951-12-18 Rca Corp Material having improved magnetic property
US2762777A (en) * 1950-09-19 1956-09-11 Hartford Nat Bank & Trust Co Permanent magnet and method of making the same
US2762778A (en) * 1951-12-21 1956-09-11 Hartford Nat Bank & Trust Co Method of making magneticallyanisotropic permanent magnets

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2946753A (en) * 1955-08-10 1960-07-26 Philips Corp Ferromagnetic material
US2946752A (en) * 1955-08-10 1960-07-26 Philips Corp Ferromagnetic material
US2955085A (en) * 1955-08-10 1960-10-04 Philips Corp Ferrites of decreased initial permeability at high frequencies
US2980617A (en) * 1956-03-13 1961-04-18 Indiana General Corp Ferrite compositions and method of making same
US3023166A (en) * 1956-08-18 1962-02-27 Philips Corp Magnetic record carrier
US5648039A (en) * 1992-04-24 1997-07-15 Tdk Corporation Process for the production of anisotropic ferrite magnets
US5945028A (en) * 1992-04-24 1999-08-31 Tdk Corporation Hexagonal system ferrite particles and their production process
US6132635A (en) * 1992-04-24 2000-10-17 Tdk Corporation Process for the production of anisotropic ferrite magnets and anisotropic ferrite magnets as well as hexagonal system ferrite particles and their production process

Also Published As

Publication number Publication date
FR67873E (fr) 1958-03-25
FR1114010A (fr) 1956-04-06
GB781633A (en) 1957-08-21

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